The ultralight Arc’teryx Cerium SL Hoody combines 850-fill down with synthetic insulation, and it was an obvious choice for our recent bikepacking trip to Mongolia’s Khangai Mountains and trek through the Altai Range. With packing space at a premium (particularly on a bike) and temperamental weather conditions, I needed a lightweight, warm, and compressible option to tackle whatever came our way. After braving unexpected storms throughout the adventure, the Cerium SL delivered on all accounts. Even though it is not as breathable or weather resistant as other fully-synthetic options, its efficient warmth has made it a staple in my pack. Below we break down the Cerium SL's warmth, weight, durability, fit and comfort, and more. To see how it stacks up, see our article on the best down jackets.  



We’ll start by noting that the Arc'teryx Cerium SL Hoody is the lighter-weight sibling of the popular Cerium LT, with 1.9 ounces of 850-fill down as opposed to 3.35 ounces in the latter. You also get a nice mix of Coreloft synthetic insulation in areas most prone to getting wet (the cuffs, under the arms, and along the shoulders and collar), which Arc’teryx calls “Down Composite Mapping.” At just 7.6 ounces for the hoody version, the Cerium SL is the lightest down jacket line that Arc’teryx makes.Arc'teryx Cerium SL down hoody (zipper 2)

During our recent Mongolia trip, the jacket kept me warm and dry even during unexpected exposure to the elements. I tend to overheat while active and typically only wear down midlayers in idle situations like early mornings around camp and transitioning when skiing; it was no different with the Cerium SL. I wore it over a light long-sleeve merino shirt and was quite comfortable even as we were hammered with snow in camp. But as soon as I started moving, I overheated, and had to stop to remove the Cerium SL in the midst of a fierce snowstorm. This isn’t a surprise—the Cerium SL is a superb insulator for its weight—but the jacket isn’t ideal during high-exertion activities. In terms of breathability, fully-synthetic options like the Arc’teryx Proton LT and Patagonia Nano-Air will perform much better.Arc'teryx Cerium SL down hoody (hiking)

Weight and Packability

Given its warmth and features, including synthetic insulation which tends to be heavier than down, the Cerium SL is impressively lightweight. At 7.6 ounces for a men’s medium, the hooded jacket truly lives up to the “SL” or “superlight” in its name. We found that an additional .2 ounces can be shaved by leaving the stuff sack at home, and the non-hooded Cerium SL is .5 ounces lighter at 7.1 ounces total.Arc'teryx Cerium SL down hoody (zipper)

Among down hoodies in the ultralight category, the leader is Montbell’s Ex Light Anorak at 6.2 ounces and with 2.3 ounces of 900-fill down. You have to sacrifice some features and trade a full-length zipper for a pullover style, but it’s very warm for its weight. Montbell also makes the full-zip Plasma 1000 without a hood, which is incredibly light at 4.8 ounces total and with 1.6 ounces of 1,000-fill down. Moving back toward the mainstream, the popular Mountain Hardwear Ghost Whisperer comes in at 7.8 ounces total and with 2.8 ounces of 800-fill down. It’s worth noting that these comparisons aren’t exactly apples to apples: all three of these jackets exclusively use down fill, whereas the Cerium SL adds synthetic on top of its 1.9-ounce down fill weight. 

In terms of packability, the Cerium SL stuffs easily into its included storage sack, compressing to about the size of a Nalgene bottle. We found the jacket can even be squished down into a smaller space—it easily packed into the lid of my Black Diamond Speed 40-liter pack and the side pocket of my Ultimate Direction Fastpack 20-liter for quick and easy access. Because it packs up so small and adds so little weight, I’ve found myself tossing the Cerium SL into my bag on almost any occasion when it looked like temperatures might dip.Arc'teryx Cerium SL down hoody (packed)

Weather Protection

I always carry a rain jacket or waterproof hardshell on backcountry trips, and I’ve never relied fully on a down jacket to keep me dry in precipitation. In Mongolia, however, there were sudden changes in the weather with little time to prepare. In addition, my outer shell’s zipper broke during a snowstorm, leaving the Cerium SL exposed to the elements. The good news is that it still kept me toasty and didn’t fully dampen as I expected. Not surprisingly, when the rain and snow persisted for extended periods of time, moisture slowly started to penetrate the jacket, particularly through the seams between the baffles.Arc'teryx Cerium SL down hoody (weather)

Throughout my experiences, the DWR finish repelled light rain and hail without wetting out, and the areas with Coreloft retained their insulating power. The nylon shell did a decent job of blocking wind, but I could definitely feel drafts between the baffles when it picked up, especially in cooler temperatures. Given the relatively meager 1.9 ounces of down and 7D shell thickness, feeling some cold and wind through the jacket was expected. As I touched on above, in almost all alpine scenarios, you’ll want to bring a waterproof shell along for maximum protection.Arc'teryx Cerium SL down hoody (rain jacket)

Hood and Other Key Features

The Arc'teryx Cerium SL Hoody is a minimalist jacket in weight and size, yet still retains important features that often are dropped in efforts to shave weight. Two roomy zippered hand pockets offer ample storage for a hat, GPS device, or even gloved hands. Both the waist hem and down-insulated hood have adjustable drawcords to seal out drafts and cinch as tight as you want. And although the hood isn’t advertised as being helmet-compatible, I was able to squeeze in a climbing helmet underneath. Lastly, a stuff sack is attached to the inside of one of the zippered hand pockets, allowing for quick access when you need to stow the jacket.Arc'teryx Cerium SL down hoody (pocket)

Durability and Build Quality

For ultralight gear like the Cerium SL, outdoor companies cut weight by using low denier threads for the shell, which results in less durable products. The 7-denier shell does feel delicate and thin, but to our pleasant surprise, it has not torn or snagged despite our rough handling. The jacket has been stuffed and pulled out of bikepacking bags, haphazardly crammed into backpacks, and even used as a blanket for my rather large dog while camping. Other than a feather poking out here and there, the Cerium SL has shown very little wear, and all zippers and cinches have held up remarkably well. To be sure, one major factor here is Arc’teryx, which makes some of the priciest jackets on the market but also excels in build and material quality and craftsmanship.Arc'teryx Cerium SL down hoody (bike)

Fit and Comfort

Arc’teryx describes the fit of the Cerium SL as “trim,” and I found this to be a little too accurate. While mostly true to size (I always get a large in Arc’teryx jackets), the hoody was noticeably snug in the waist and shoulders. The fit makes it easy to wear under a shell with no bunching, but it did restrict overall movement a bit. This was particularly noticeable while scrambling on fourth class terrain. Unlike many synthetic jacket options, it doesn’t have much give or stretch, and I also found it to be a bit shorter than I prefer (the waist rides up when reaching). Therefore, the Cerium SL was most comfortable during inactive times like sitting around camp or huddled in our tent at the end of the day.Arc'teryx Cerium SL down hoody (tent 2)

What We Like

  • Ultralight and packs down very small, yet still comes with features like zippered hand pockets and a cinchable hood and waist.
  • The synthetic insulation in areas prone to wetting out kept me warm and dry even in severe weather.
  • The clean lines and precise stitching give this jacket a sleek look.

What We Don’t

  • A little too trim and snug for our taste. I had trouble reaching overhead and found that the jacket rode up at times.
  • The jacket can be drafty in cold winds, especially through the stitching between baffles.
  • Doesn’t excel in breathability, although it’s not intended for sustained active use like other fully-synthetic options.

Arc'teryx Cerium SL down hoody (van)

Comparison Table

Jacket Price Weight Fill Fill Weight Denier
Arc'teryx Cerium SL Hoody $349 7.6 oz. 850-fill down 1.9 oz. 7D
Arc'teryx Cerium LT Hoody $379 10.8 oz. 850-fill down & Coreloft 3.35 oz. & 80 g/m2 20x10D
Mountain Hardwear Ghost Whisperer $350 7.8 oz. 800-fill down 2.8 oz. 7x10D
Montbell Plasma 1000 Alpine Parka $439 8.4 oz. 1,000-fill down 3.4 oz. 7D
Montbell Ex Light Anorak $269 6.2 oz. 900-fill down 2.3 oz. 7D

The Competition

In terms of competitors, we’ll start in-house with one of Arc’teryx’s most popular jackets: the Cerium LT Hoody. Both Cerium jackets use Down Composite Mapping for a combination of 850-fill down and Coreloft synthetic, which still is a rarity in the jacket world and a nice design feature. The LT version is heavier at 10.8 ounces, warmer with 3.35 ounces of 850-fill down, and more durable with a 20x10D ripstop nylon shell as opposed to the thin 7D fabric on the SL. All things considered, the Cerium LT is the better all-rounder: we’ve found it ideal for staying warm on backpacking trips, under a shell for downhill skiing, and worn casually around town (for more information, see our in-depth Cerium LT review). But the Cerium SL is best for ultralighters and those counting ounces, and its warmth and weather protection exceeded expectations during our testing. Both offer outstanding build quality and have a high-end look and feel.Arc'teryx Cerium SL down hoody (coffee)

Mountain Hardwear’s Ghost Whisperer gives the Cerium SL a run for its money when it comes to warmth relative to weight. Its sub-8-ounce weight and 800-fill down give it similar warmth, while its full hood, two zippered hand pockets, and side cinch make it competitive in the features department as well. That said, the Ghost Whisperer’s hood isn’t adjustable and its cuffs are wide and lacking in stretch, making the jacket a bit less effective at sealing out the cold. And when it comes to weather protection, the Cerium SL’s added synthetic insulation has proven invaluable. It’s a close call and both jackets are the same price at $350, but we give a slight nod to the tried-and-true Ghost Whisperer, and particularly if you prefer a more generous fit.Arc'teryx Cerium SL down hoody (mongolia)

If shaving weight is your ultimate goal, it’s hard not to be impressed by Montbell’s Plasma 1000. This unique jacket has 1.6 ounces of ultra-premium 1,000-fill down, and weighs only 4.8 ounces total for a non-hoody version. Keep in mind that this truly is a minimalist piece with no hand pockets, no hood, very few adjustments, and build quality that is good but a step down from Arc’teryx. If you’re willing to give up the full zipper, the Montbell Ex Light Anorak has 2.3 ounces of 900-fill down and comes in at 6.2 ounces total—1.4 ounces less than the Cerium SL Hoody—plus the jacket is cheaper at $269. You do sacrifice in features and everyday appeal, but Montbell is popular among serious outdoorspeople and for good reason. 

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